Anaerobic bioreactors have typically included a bioreactor tank for containing a suspension of naturally forming anaerobic bacteria granules which is a mixture or consortium of bacteria adapted for digesting biological oxygen demand (BOD) or biological waste in wastewater. Those skilled in the art refer to these anaerobic bacteria granules as “microbial consortia particles” or “microbial consortia culture particles” or “active microbial consortia particles” in the case of viable, active anaerobic bacteria granules. The use of such microbial consortia particles for digesting waste in wastewater is well known to those who are skilled in the art. The microbial consortia particles are maintained in a fluidized or expanded or upflow blanket bed by an upwelling flow of wastewater which generally enters the lower end of the bioreactor tank in a generally distributed fashion. Treated wastewater generally exits a typical bioreactor tank in an overflow discharge at the upper end of the bioreactor. An anaerobic bioreactor tank using a culture of microbial consortia particles is most effective if the particles interact with the wastewater in a fluid bed environment. The microbial consortia particles typically have an average size ranging in diameter approximately between 0.5 mm and 3 mm. The microbial consortia particles interact with organic waste and produce various biogas byproducts including methane and carbon dioxide. They also add to their biomass as they digest organic waste. The amount of organic waste in wastewater is measured by biological oxygen demand (BOD) or chemical oxygen demand (COD). Biological oxygen demand (BOD) is a measurement that describes the organic loading in waste water and is well known to those skilled in the art. Typically, the preferred BOD measurement used by those skilled in the art is a five day test for BOD measurement. Chemical oxygen demand (COD) is also a measurement that describes the organic loading in waste water and also is well known to those skilled in the art. COD measurements are more commonly used in the art of anaerobic digestion of organic waste. Methane is not soluble in water, so methane bubbles often form on the surfaces of the microbial consortia particles causing the granules to become buoyant and thus rise within the fluidized bed column. Typically, the interior of the bioreactor tank is provided with various baffle structures typically in the form of inverted conical or inclined plate structures. The purpose of these baffle structures is to contact the microbial consortia particles and impede their migration to the surface of the fluidized bed column. The contact of the granules with baffle structure causes the microbial consortia particles to shed their buoyant methane bubbles and thus impede their migration to the surface of the water and the overflow discharge of the bioreactor. Even with the use of such baffles and other internal selectors or settlers, the tendency of buoyant granules to escape with an overhead discharge is a significant constraint for prior art bioreactors. This constraint reduces the capacity of prior art bioreactors below the biological capacity of microbial consortia particles within a prior art bioreactor. Such internal structures also occupy a significant portion of the volume of prior art bioreactors. This constraint imposed by the need to prevent the escape of microbial consortia particles from a bioreactor tank can limit the capacity, of a bioreactor tank to about 50% of the capacity of a fully charged bioreactor. Accordingly, what is needed is an anaerobic wastewater treatment system in which the potential capacity of a bioreactor tank is substantially fully exploited and wherein the constraint imposed by the need to retain microbial consortia particles is eliminated.